Example systems for adjusting the toner concentration of liquid toner suitable for liquid-development electrophotographic apparatuses include a system in which when the quantity of toner reaches a predetermined level, blank printing is performed so as to accelerate consumption of carrier.(see Patent Document 1); and a system in which residual toner collected from a photosensitive drum is physically separated into high-concentration toner and low-concentration toner (see Patent Document 2).
Patent Document 1: Japanese Patent Application Laid-Open (kokai) No. H10-63103
Patent Document 2: Japanese Patent Application Laid-Open (kokai) No. H10-282796
In a conventional liquid-development electrophotographic apparatus, an electrostatic latent image is formed on a photosensitive drum by means of a well-known image forming process; liquid toner consisting of toner particles of a single color and carrier is supplied to the drum so as to develop the electrostatic latent image, to thereby form a toner image; and the toner image is transferred to an intermediate transfer member. The single-color toner image transferred to the intermediate transfer member mixes with other single-color toner images to thereby form a color image, which is then transferred to a predetermined printing medium.
When image formation is performed in a liquid-development electrophotographic apparatus having the above-described configuration, toner particles contained in liquid toner are consumed at a rate determined by the area of an image portion. In contrast, carrier is generally consumed at a constant rate irrespective of the area of images. Following printing, the residual liquid toner is collected, and is again used for printing. At that time, the concentration of the liquid toner is adjusted to a fixed level by means of a toner concentration adjustment apparatus. Thus, the toner concentration to be adjusted by means of the toner concentration adjustment apparatus always change in accordance with printed images.
A conventional toner concentration adjustment apparatus for such a liquid-development electrophotographic apparatus will be described with reference to FIG. 7. An electrostatic latent image formed on the surface of a photosensitive drum 2 is developed by liquid toner transferred from a development roller 3, so that a toner image is formed. The toner image is transferred to an intermediate transfer member 1. Liquid toner (residual toner) which remains on the surface of the photosensitive drum 2 after transfer of the toner image to the intermediate transfer member 1 is scraped off by means of a collection blade 5a, and is collected in a collection pot 6a. Since the greater portion of toner particles forming the image is transferred to the surface of the intermediate transfer member 1, the liquid toner collected in the collection pot 6a is mainly composed of carrier. Moreover, liquid toner which remains on the surface of the development roller 3 after transfer of the liquid toner to the photosensitive drum 2 is scraped off by means of a collection blade 5b, and is collected in a collection pot 6b. 
The liquid toner collected in the collection pot 6a and the liquid toner collected in the collection pot 6b are both fed to a toner concentration adjustment apparatus 50. In the toner concentration adjustment apparatus 50, the liquid toner is mixed with high-concentration toner (liquid toner which contains toner particles at a greater proportion than does the liquid toner used for printing) within a concentration adjustment pot 51 under monitoring by a toner concentration detection mechanism 54. The high-concentration toner is supplied from a high-concentration toner replenishment mechanism 53. In this manner, toner particles lost in a printing process are replenished so as to increase toner concentration; and liquid toner having a predetermined toner concentration is transferred, as regenerated toner, to a supply pot 7, and is then used again.
The high-concentration toner to be mixed with the liquid toner in the concentration adjustment pot must have properties of liquid toner. Thus, the concentration of the high-concentration toner cannot be increased to a level at which the proportion of toner particles contained in the high-concentration toner exceeds about 30%. Therefore, when the high-concentration toner is supplied for concentration adjustment, not only the necessary toner particles, but also carrier is supplied, so that the quantity of regenerated liquid toner increases on the whole.
Moreover, in the case where toner particles are consumed at a large rate in a printing process because of, for example, a large designated printing area, the quantity of toner particles to be replenished becomes large as compared with the residual quantity of carrier, whereby a larger quantity of the high-concentration toner is needed for concentration adjustment.
As a result, in the toner concentration adjustment apparatus 50, which produces regenerated liquid toner, the quantity of the regenerated liquid toner increases, with the possible result that the liquid toner spills over from the concentration adjustment pot 51.